This invention relates generally to aircraft flight control, and more particularly concerns method and apparatus to aid in overcoming problems of aircraft control that arise due to the existence of wind shear.
Weather and wind have always been of great importance to the aircraft pilot. From the experience of the Wright Brothers, who chose a place with favorable wind and weather for their experiments, to the modern jet pilot, most of the weather factors have been solved by technology and the environment of the modern jet airliner, with the use of high altitudes, radar, and the advanced state of knowledge called aerodynamics.
Along with the advance of large, massive airplanes there has emerged a problem area called "wind shear". It has been with us from the beginning of aviation, but becomes a problem of major proportions when a massive airplane depends on its own acceleration to deal with it. Consequently, there have been many accidents involving wind shear, and very likely many caused by it which were not attributed to it. Only recently has its importance been explored and appreciated. The more information investigators compile, the more it is realized that wind shear is a very serious problem. It is also complex enough to elude any simple easily understood solution.
While pilots commonly add some airspeed to accommodate a known wind shear condition, nothing in aviation today provides for the unanticipated wind shear. The only forewarning a pilot can receive is from another pilot reporting its existence from flying through it himself. Even if forwarned, the pilot only has his own guesswork to rely on to deal with it, and the condition may change or even reverse itself by the time he actually encounters it. There are no means presently in existence on board any aircraft which provides the pilot with information on his present condition as regards windshear, let alone what may be ahead. He is totally committed to fly his approach maintaining an airspeed, whether manually or on auto-pilot. These problems can even be compounded by the use of auto-pilot and auto-throttle.
A wind shear which leaves the airplane thrust-deficient near the ground can be particularly dangerous, as described in the following:
As the airplane descends on the final approach he encounters a steadily increasing tail-wind, which requires a constant power, slightly above normal to maintain constant airspeed. This occurs whether using auto-throttle or manual control. A distance short of the runway, the tail-wind decreases and his airspeed rises calling for a decrease in power to hold his desired airspeed. Now, still short of the runway in a slight but steady head-wind, the airspeed reduces rapidly due to low power, and the pilot now has to add power to land on the runway, but it takes time for the engines to accelerate. He has done everything according to accepted practice, but he had another accident attributed to "pilot error", because he didn't have enough airspeed to reach the runway. This type of wind shear can be particularly insidious, because this can occur without any significant turbulence, and with such a gradual variance as to be barely perceptible. There have been several recent accidents, of this very nature.
This is but one illustration of the problems associated with wind shear. It is the object of my invention to solve such problems and produce a system and procedure whereby these problems are inherently solved within the system and procedure as far as feasible.